1. Field of the Invention
The present invention relates to an activation device for a piston/cylinder unit, in particular for a gas spring, whose movement can be selectively inhibited and includes a valve device for operational motion of a piston rod and an activation device for operating the valve device.
2. Description of the Prior Art
Gas springs whose movement can be selectively inhibited are employed, for example, in chairs which have a seat back which is spring-supported and can be rigidly held by the selective inhibiting function of the gas spring. A chair user does not, however, continuously adopt the same posture on the chair. The seat back position can be very easily matched to the instantaneous seating position by the activation device. The user may also, for example, lean forward so that the seat back has no contact with the back of the user. If the activation device for the gas spring on the seat back is actuated while the user is in this position, the seat back is accelerated by the gas spring in the direction of the user""s back and impinges on it. This operational behavior is undesirable. German reference DE 69 35 911 U1 describes a gas spring which has a divided activation push-rod, a spring being arranged between the two activation push-rod sections. Slower opening of the blocking valve within the gas spring is achieved using the spring.
A similar activation means is described in German reference DE 36 15 688 A1 in which a valve cross section of the blocking valve changes over the stroke path of the activation push-rod. The throttling associated with this valve only permits the piston rod to extend slowly at the beginning of the stroke path of the activation push-rod and then increasingly more rapidly toward the end of the activation push-rod stroke length. Although the problem of undesireable contact with the seat back is diminished by both of these prior art types of gas springs, it is by no means reliably prevented.
GB 2 304 036 A1 (GB ""036) relates to an activation device which has two switching inputs. The activation push-rod can, on the one hand, be activated by means of a Bowden cable. In addition, the seat support is in connection with the activation device such that when the seat support is unloaded, the gas spring is always in the unlocked operating function is always adopted on the gas spring independently of the switching condition of the Bowden cable. An activation appliance, which acts directly on the activation push-rod and which is embodied as a rocker arm is used for activating the Bowden cable. An essential feature is that the seat panel is required to pivot for recording the loading condition. However, this imposes a limitation to the chair design. Comfortable chairs often feature a seat inclination adjustment. Such a seat inclination adjustment would have a substantial influence on the function of the activation device of GB ""036.
The object of the present invention is to provide a piston/cylinder unit, in particular a gas spring, having a braked operating motion independent of stroke.
According to the present invention, the object is achieved by a loaded gas spring having a load contact device connecting an actuation device to the valve device of the gas spring piston for the purpose of changing the adjustability of the valve device. When using a chair, the load contact device is associated with the advantagexe2x80x94for the user of the chairxe2x80x94that when the seat back is not in contact with his back, the inhibited movement position of the gas spring cannot be canceled by a switching movement on the actuation device. If, however, the seat back is in contact with the user""s back, then the load contact device permits a comfortable seat back adjustment using the actuation device. The seat back does not strike the user because it is already in contact with his back.
The load contact device may include a slide which can move relative to the gas spring. The slide is in effective connection with the actuation device at a fixed location. When the seat back is loaded by the user, the slide moves the actuation device into a position from which an effective actuation motion can take place.
To continually ensure a defined operating position of the load contact device, the slide is preloaded by a spring in the direction of a disengaged position of the load contact device.
It should, as far as possible, be possible to combine the load contact device according to the invention with a standard gas spring. For this purpose, an activation push-rod for the valve device is divided in two parts in the axial direction. A first part of the activation push-rod is contained in the gas spring as a series production item. A second part, which has the approximate axial length of the load contact device, can then be used as an adapter.
To obtain increased design freedom in the choice of the spring for the load contact device, the load contact device has a spring support, which is firmly connected axially to the gas spring. As an alternative, the spring may also be arranged to engage on an end surface of the gas spring.
The spring support may thus be formed by a threaded sleeve. The threaded sleeve permits adaptation of the position of the load contact device to compensate for possible manufacturing tolerances.
To ensure that the gas spring has a reliable fastening to the load contact device, an axial stop may be used to limit the displacement path of the load contact device. In this arrangement, the axial stop contacts the spring support.
The slide, an end of the slide for supporting the spring urgency and the axial stop for receiving the other end of the spring form a casing of the load contact device, in which the spring is enclosed. This allows the load contact device to be manufactured as a structural unit independently of the technical application and the gas spring can be manufactured as a separate sub-assembly.
In addition, the end of the slide forms a further axial stop acting in a direction opposite to that of the first axial stop, so that the operational movement of the slide is limited in both directions and the spring is not necessarily preloaded to provide the blocking function.
In a particularly simple embodiment, the spring is supported on the cylinder. The major advantages of this solution is that it is possible to dispense with a separate casing. Furthermore, the use of the load contact device according to this embodiment requires practically no loss of the stroke of the conventional piston/cylinder unit.
The spring support may be fastened to the cylinder, the spring being supported on the unit composed of the slide and the activation device.
Furthermore, the slide may be supported on the piston rod. The piston rod features a very high-quality surface so that good guidance is provided. It is, furthermore, possible to dispense with a fastening thread for the load contact device.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.